1. Field of the Invention
The present invention relates to scratch-resistant, electrically conductive or anti-static coatings for electrically non-conductive moulded parts made of glass or plastics materials. More particularly, the coatings are made from combinations of partially hydrolyzed silanes and conductive polythiophene coatings.
2. Description of the Prior Art
Moulded parts made of glass and plastics material are electrostatically charged by friction or the application of charges (for example electron radiation in television picture tubes). These charges attract dust particles so that the moulded parts rapidly gather dust. Therefore, these moulded parts must be protected against electrostatic charging. This can be achieved, for example, by means of an antistatic coating with a surface resistance of &lt;10.sup.10 .OMEGA./.quadrature.. If the surface resistance of the coatings is &lt;1,000 .OMEGA./.quadrature., the antistatic effect is accompanied by a shielding effect against electromagnetic/electrostatic radiation.
For practical uses these coatings must also possess adequate mechanical resistance and adhesive strength. In particular, when glass is used as carrier, (the layers must be sufficiently scratch-resistant in order that, during the cleaning of the coated surfaces, damage to the coating, and thus loss of the antistatic or conductive effect, can be avoided.)
The literature has disclosed electrically conductive polymers, for example, polythiophenes, for the production of antistatic or conductive coatings.
From EP-A 440 957 and DE OS 4 211 459, it is known to use coatings of polythiophene containing a polythiophene salt polythiophene.sup.+ /An.sup.-, wherein the polythiophene.sup.+ group contains positively charged and uncharged recurring units of the formula (I):
wherein
n represents an integer from 5 to 100, and PA1 R.sub.1 and R.sub.2, independently of one another, represent hydrogen, an optionally substituted alkyl group having 1 to 20 carbon atom, --CH.sub.2 --OH, or an aryl group having 6 to 14 carbon atoms, or PA1 R.sub.1 and R.sub.2, together, represent an optionally substituted alkylene group having 1 to 20 carbon atoms, and PA1 An.sup.- means a polyanion, PA1 for the production of conductive or antistatic coatings. PA1 R' means an alkyl group having 1 to 4 carbon atoms, a phenyl- or vinyl group, and R" is an alkyl group having 1 to 4 carbon atoms. Methyltriethoxysilane is preferred. PA1 R" has the meaning given above.
The use of these polythiophene salts for the antistatic finishing of glass has been described in DE-OS 4 229 192.
However, it has been shown that in practice these coatings are not sufficiently scratch-resistant for some applications. Therefore, the object existed of modifying the polythiophene coatings in such manner as to obtain a scratch resistance which is adequate under practical conditions.
In DE-A 19 524 132, it is proposed to add binding agents which cure through ionizing radiation to the polythiophene salt coatings in order to improve scratch resistance. However, these combinations are also insufficiently scratch-resistant for practical applications of the conductive coatings, e.g.; as an antistatic finish for cathode ray tubes for televisions or monitors.
Additionally, EP-A 17 187 has disclosed scratch-resistant coatings based on hydrolyzed silanes. However, it has been shown that these, are incompatible with the conductive polythiophene salt coatings.